struct initialization from incompatible pointer type

Incompatible pointer type error using structs

c++ pointers struct

I am new to programming. I am trying to learn C and pointers, but it is giving me much trouble. I got the following error trying to implement a singly linked list. I searched online, and I couldn't find someone who had an error just like mine, or perhaps I just didn't couldn't make sense of it with my problem.

The following is the error I received:

warning: incompatible pointer types initializing 'NODE *' (aka 'struct node *') with an expression of type 'struct NODE ' [-Wincompatible-pointer-types] NODE temp = (*l)->head;

In main, I passed the address of the variable of type LIST. So, I thought I had to dereference 'l', to get the address of where the LIST type is located, then I had to dereference with an arrow to get the address of where the NODE is located. Where am I confused? I do appreciate the help.

Below you will see the code I have written:

Best Solution

I guess your problem is here :

just remove struct keyword before NODE

Also you need to initialize the head with NULL to make this condition to wwork

so when you create your list add l->head = NULL;

And the last one (i hope) when you create your first node, you forget to assign head to it, and return in order not to add the first element twice

And BTW, don't cast malloc results in C

C++ – a smart pointer and when should I use one

This answer is rather old, and so describes what was 'good' at the time, which was smart pointers provided by the Boost library. Since C++11, the standard library has provided sufficient smart pointers types, and so you should favour the use of std::unique_ptr , std::shared_ptr and std::weak_ptr .

There was also std::auto_ptr . It was very much like a scoped pointer, except that it also had the "special" dangerous ability to be copied — which also unexpectedly transfers ownership. It was deprecated in C++11 and removed in C++17 , so you shouldn't use it.

A smart pointer is a class that wraps a 'raw' (or 'bare') C++ pointer, to manage the lifetime of the object being pointed to. There is no single smart pointer type, but all of them try to abstract a raw pointer in a practical way.

Smart pointers should be preferred over raw pointers. If you feel you need to use pointers (first consider if you really do), you would normally want to use a smart pointer as this can alleviate many of the problems with raw pointers, mainly forgetting to delete the object and leaking memory.

With raw pointers, the programmer has to explicitly destroy the object when it is no longer useful.

A smart pointer by comparison defines a policy as to when the object is destroyed. You still have to create the object, but you no longer have to worry about destroying it.

The simplest policy in use involves the scope of the smart pointer wrapper object, such as implemented by boost::scoped_ptr or std::unique_ptr .

Note that std::unique_ptr instances cannot be copied. This prevents the pointer from being deleted multiple times (incorrectly). You can, however, pass references to it around to other functions you call.

std::unique_ptr s are useful when you want to tie the lifetime of the object to a particular block of code, or if you embedded it as member data inside another object, the lifetime of that other object. The object exists until the containing block of code is exited, or until the containing object is itself destroyed.

A more complex smart pointer policy involves reference counting the pointer. This does allow the pointer to be copied. When the last "reference" to the object is destroyed, the object is deleted. This policy is implemented by boost::shared_ptr and std::shared_ptr .

Reference counted pointers are very useful when the lifetime of your object is much more complicated, and is not tied directly to a particular section of code or to another object.

There is one drawback to reference counted pointers — the possibility of creating a dangling reference:

Another possibility is creating circular references:

To work around this problem, both Boost and C++11 have defined a weak_ptr to define a weak (uncounted) reference to a shared_ptr .

[Solved]-how to fix problem with initialization from incompatible pointer type-C

error: initialization from incompatible pointer type [-werror=incompatible-pointer-types] .read = read_proc, error: initialization from incompatible pointer type [-werror=incompatible-pointer-types] .write = write_proc,

the signature expected of the read function is

the signature expected of the write function is

( https://linux-kernel-labs.github.io/refs/heads/master/labs/device_drivers.html )

the the names of the functions and of their parameters do not matter, but the return type and the number, order, and types of the arguments all do.

your read_proc() doesn't appear to match at all. i guess its possible that it's closer to right for some other version of the kernel than the doc i linked describes. your write_proc() function is closer, but unsigned long is probably not the same type as size_t , and void * is probably not the same type as loff_t * . either one of those discrepancies is enough for a pointer type mismatch, and they could cause genuine behavioral issues.

error: dereferencing pointer to incomplete type ‘struct proc_dir_entry’ our_proc_file->read_proc = read_proc;

it is not necessary to have the definition of struct proc_dir_entry to declare a pointer to that type, but it is necessary to have a definition in order to access members of an instance, via such a pointer or otherwise. at the point where you attempt to do

, no such definition is in scope. possibly you have forgotten to include the appropriate header. alternatively, you may have misspelled the structure tag.

Related Query

how to fix problem with initialization from incompatible pointer type
How to fix passing argument 1 of 'count' from incompatible pointer type
How to resolve initialization from incompatible pointer type
Initialization from incompatible pointer type warning with an array allocated on stack
typedef function pointer -> initialization from incompatible pointer type
C (gcc) warning: initialization from incompatible pointer type when calling pthread_cleanup_push()
incompatible integer to pointer conversion returning 'int' from a function with result type 'void *'
initialization from incompatible pointer type during array initialization
Getting context on initialization from incompatible pointer type
proc_dir_entry warning: initialization from incompatible pointer type [enabled by default]
Initialization from incompatible pointer type when assigning struct file_operations fields
How to place string into an array in c. Also why do i get return from incompatible pointer type error?
initialization of 'const char **' from incompatible pointer type 'char *'
Function pointers - outside library, warning: initialization from incompatible pointer type
How to return a pointer with a type from a void pointer, when the type is known
Pointer that points to return of function. Initialization from incompatible pointer type
Defining a vector of struct and passing it as pointer in C - error: initialization from incompatible pointer type
How do I fix a segmentation fault with a pointer being passed from a function in C?
C how can i resolve assignment from incompatible pointer type when using struct* = struct
How can I fix incompatible pointer to integer conversion assigning to 'int' from 'void *'
how to fix incompatible pointer types passing 'char [16]' to parameter of type 'FILE *' (aka 'struct __sFILE *') [-Wincompatible-pointer-types]
avr-gcc warning: initialization from incompatible pointer type
warning: initialization from incompatible pointer type
initialization from incompatible pointer type - C structs
Initialization from incompatible pointer type when constructing a GTK combobox
Pointer Functions in C: initialization of foo from incompatible pointer type
C,GCC warning: initialization from incompatible pointer type
Warning: passing argument 2 of 'transform_labels' from incompatible pointer type [-Wincompatible-pointer-types]|
How to point at incompatible pointer type in C?
error: passing argument 1 of ‘kthread_create_on_node’ from incompatible pointer type

More Query from same tag

cuda file did not link with function defined in C file
C - Float Imprecision, How to lock the decimal places for calculations?
NSUInteger C Array
Using fread properly
STM32L011 cannot set USART in rx mode
hiredis getting err 1 REDIS_ERR_IO No such file or directory
Get List of Time Zones Across Platforms in C
How can array name and the address of the array name both prints the same value?
Constant Pointers vs Pointers to Constant Strings
Aligning printf() variables and decimals in C
Why is it not possible to replace stdout with pipe output directly?
why buffer overflow happens?
Code that prints only five-digit numbers with spaces
gcc undefined reference when I know the references are correct
Activate and deactivate usb device in c?
Move node to a new index in a linked list
IPMI: How to find the threshold values using ipmimonitoring-sensors.c
My consumer thread isn't reading my producer thread's products correctly
Calculate how many hours since the epoch?
Don't understand simple C Program if/else result
How much memory would be freed if pointer is changed in C?
Ordered Binary Tree insert
Simplifying a Recursive Function
Changing an inputted integer into a defined constant value
Setting userdata as namespace in Lua
How to get number of NIC RX rings in Linux
can't compile c code
Inlining typedef for a function returning a function
Error: Variable-sized object may not be initialized
How to get the expected answer